When drilling a wellbore, the drill bit and drill string, as well as other associated equipment, are subject to various forces. For example, during drilling, the drill bit is subject to a counterforce in the uphole direction applied by the formation, rotational force from the motive source being used to drill, excess torque from the drill string, vibrational forces from the drill string and/or other equipment located uphole from the drill bit, and/or other similar forces. These and other types of forces can briefly lift the drill bit from the bottom of a wellbore (e.g., creating “bit whirl”), and/or cause the drill bit to be subjected to undesirable lateral forces, which can result in the drill bit and/or drill string becoming stuck, an undesired deviation of the direction in which the wellbore is drilled, and other losses in drilling efficiency, as well as possible wear and/or damage to equipment. Further, in addition to lifting and/or deviating the drill bit, vibration of the drill string can cause the drill string, itself, and/or other components associated therewith, to contact the borehole wall, becoming stuck, damaged, and/or reducing drilling efficiency.
As such, during drilling operations, it is important to maintain an adequate “weight-on-bit” to counteract the tendency of the drill bit to be lifted from the bottom of the wellbore and/or to deviate from the desired direction of drilling. During vertical drilling operations, the weight of the drill string, itself, as well as the weight of one or multiple drill collars, stabilizers, and/or other components, placed just above the drill bit in a bottomhole assembly, provides significant weight to the drill bit, which not only maintains contact between the bit and the formation to reduce deviation, but also improves the rate of drilling. However, during horizontal drilling and/or drilling in any other non-vertical direction, the weight of the drill string, bottomhole assembly, and/or other components associated with the drill string provides significantly less benefit, and in many cases, may hinder directional drilling operations through undesired contact between the drill string and/or any tools or components therealong and the borehole wall, especially when passing through curved/bent portions of the wellbore.
Conventionally, during horizontal drilling operations, a thruster, tractor, and/or shock absorber can be installed, proximate to the drill bit. A typical thruster will use hydraulic elements (e.g., pistons and cylinders) to apply a constant force to the drill bit to maintain the bit on the bottom of the wellbore. A tractor will use hydraulic elements to pull and/or push on the drill string or drill bit. A shock absorber will include resilient and/or similar elements designed to cushion all components on one side of the shock absorber from forces received from components on the opposing side. Each of these types of tools, used singularly or in combination, provides some effectiveness when attempting to improve drilling efficiency, maintain a drill bit on the bottom of a wellbore, and reduce the effect of drill string vibration on a drill bit. However, a need exists for devices specifically designed to apply an uphole force in the direction of the drill string to reduce the inefficiencies and difficulties caused by drill string vibration on the drill string itself, not simply the drill bit. A need also exists for devices and methods for simultaneously applying a downhole force to maintain an acceptable weight-on-bit, and an uphole force usable to control drill string vibrations.